Low-viscosity allophanates containing actinically curable groups

ABSTRACT

A process for preparing binders containing allophanate groups which contain, at the oxygen atom of the allophanate group that is bonded via two single bonds, organic radicals with activated groups capable of participating in a polymerization reaction with ethylenically unsaturated compounds on exposure to actinic radiation; the process includes reacting A) one or more compounds containing uretdione groups with B) one or more OH-functional compounds which contain groups capable of participating in a polymerization reaction with ethylenically unsaturated compounds on exposure to actinic radiation, and C) optionally further NCO-reactive compounds, and D) in the presence of one or more compounds containing phenoxide groups, as catalysts. The binders can be used in preparing coatings, coating materials, coating compositions, adhesives, printing inks, casting resins, dental compounds, sizes, photoresists, stereolithography systems, resins for composite materials and sealants.

CROSS REFERENCE TO RELATED PATENT APPLICATION

The present patent application claims the right of priority under 35U.S.C. §119 (a)-(d) of German Patent Application No. 10 2004 012 903.7,filed Mar. 17, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to low-viscosity reaction products ofpolyisocyanates which contain activated groups which react, withpolymerization, with ethylenically unsaturated compounds on exposure toactinic radiation, to a process for preparing them and to their use incoating compositions.

2. Description of the Prior Art

The curing of coating systems which carry activated double bonds byactinic radiation, such as UV light, IR radiation or else electronbeams, is known and is established in industry. It is one of the mostrapid curing methods in coating technology.

Because of the environmental and economic requirements imposed on moderncoating systems, that they should use as little organic solvents aspossible, or none at all, for adjusting the viscosity, there is a desireto use coatings raw materials which are already of low viscosity. Knownfor this purpose for a long time have been polyisocyanates with anallophanate structure as are described, inter alia, in EP-A 0 682 012.

In industry these substances are prepared by reacting a monohydric orpolyhydric alcohol with excess aliphatic and/or cycloaliphaticdiisocyanate (cf. GB-A 994 890, EP-A 0 000 194 or EP-A 0 712 840). Thisis followed by removal of unreacted diisocyanate by means ofdistillation under reduced pressure. According to DE-A 198 60 041 thisprocedure can also be carried out with OH-functional compounds havingactivated double bonds, such as hydroxyalkyl acrylates, althoughdifficulties occur in relation to the preparation of particularlylow-monomer products. Since the distillation step has to take place attemperatures up to 135° C., in order to be able to lower the residueisocyanate content sufficiently (<0.5% by weight of residue monomer), itis possible for double bonds to react, with polymerization, underthermal initiation, even during the purification process, meaning thatideal products are no longer obtained.

The preparation of low-monomer-content, allophanate-containing,polyurethane-based, radiation-curing binders is described in EP-A 0 867457 and U.S. Pat. No. 5,739,251. These binders, however, do not carryactivated double bonds but instead carry unreactive allyl ether groups(structure R—O—CH₂—CH═CH₂). It is therefore necessary to add reactivediluents (low molecular weight esters of acrylic acid), which introducethe required UV reactivity.

EP-A 0 825 211 describes a process for synthesizing allophanatestructures from oxadiazinetriones, although no radiation-curingderivatives having activated double bonds are known. All that ismentioned is the use of maleate- and/or fumarate-containing polyesters;the possibility of radiation curing is not described.

U.S. Pat. No. 5,777,024 describes the preparation of low-viscosityradiation-curing allophanates by reacting hydroxy-functional monomerswhich carry activated double bonds with isocyanate groups ofallophanate-modified isocyanurate polyisocyanates. The allophanate-boundradicals are saturated as a result.

The formation of allophanate compounds by ring opening of uretdioneswith alcohols is known in principle as a crosslinking mechanism inpowder coating materials (cf. Proceedings of the InternationalWaterborne, High-Solids, and Powder Coatings Symposium 2001, 28th,405-419, and also US-A 2003 0153 713). Nevertheless, the reactiontemperatures required for this purpose are too high (≧120° C.) for atargeted preparation of radiation-curing monomers based on allophanatewith activated double bonds.

Historically the direct reaction of uretdione rings with alcohols toallophanates was first investigated for solventborne, isocyanate-free,2K [2-component] polyurethane coating materials. Without catalysis thisreaction is of no technical importance, owing to the low reaction rate(F. Schmitt, Angew. Makromol. Chem. (1989), 171, pp. 21-38). Withappropriate catalysts, however, the crosslinking reaction betweenHDI-based uretdione curatives and polyols is said to begin at 60-80° C.(K. B. Chandalia; R. A Englebach; S. L. Goldstein; R. W. Good; S. H.Harris; M. J. Morgan; P. J. Whitman; R. T. Wojcik, Proceedings of theInternational Waterborne, High-Solids, and Powder Coatings Symposium,(2001), pp. 77-89). The structure of these catalysts has not beenpublished to date. Commercial products prepared by utilizing thisreaction are also undisclosed to date.

In summary it may be stated that the preparation of low-viscosityradiation-curing allophanates by ring-opening reaction of alcoholscarrying activated double bonds with uretdiones at temperatures below100° C. is not disclosed in detail in the prior art.

SUMMARY OF THE INVENTION

The present invention provides a process for preparing binderscontaining allophanate groups which contain, at the oxygen atom of theallophanate group that is bonded via two single bonds, organic radicalswith activated groups capable of participating in a polymerizationreaction with ethylenically unsaturated compounds on exposure to actinicradiation; the process includes reacting

-   A) one or more compounds containing uretdione groups with-   B) one or more OH-functional compounds which contain groups capable    of participating in a polymerization reaction with ethylenically    unsaturated compounds on exposure to actinic radiation, and-   C) optionally further NCO-reactive compounds, and-   D) in the presence of one or more compounds containing phenoxide    groups, as catalysts.

The present invention also provides a method of preparing coatings,coating materials, adhesives, printing inks, casting resins, dentalcompounds, sizes, photoresists, stereolithography systems, resins forcomposite materials and sealants. The method includes combining theabove-described binders containing allophanate groups and one or moreadditives selected from the group consisting of UV absorbers, HALSstabilizers, pigments, dyes, fillers, levelling additives,devolatilizing additives, catalysts, and combinations thereof.

The present invention additionally provides coating compositions thatinclude

-   a) one or more of the above-described binders containing allophanate    groups,-   b) optionally one or more polyisocyanates containing free or blocked    isocyanate groups, which are free from groups capable of    participating in a polymerization reaction with ethylenically    unsaturated compounds on exposure to actinic radiation,-   c) optionally other compounds, different from those of a), which    contain groups capable of participating in a polymerization reaction    with ethylenically unsaturated compounds on exposure to actinic    radiation, and optionally contain free or blocked NCO groups,-   d) optionally one or more isocyanate-reactive compounds containing    active hydrogen,-   e) initiators,-   f) optionally solvents and-   g) optionally auxiliaries and additives.

The present invention further provides substrates coated with coatingsobtained from the above-described binders containing allophanate groups.

DETAILED DESCRIPTION OF THE INVENTION

Other than in the operating examples, or where otherwise indicated, allnumbers or expressions referring to quantities of ingredients, reactionconditions, etc. used in the specification and claims are to beunderstood as modified in all instances by the term “about.”

It was an object of the present invention to provide a process forpreparing binders containing allophanate groups and having activateddouble bond(s) which is accomplished with temperatures of below 100° C.,the products thus obtainable preferably having viscosities at 23° C., inundiluted form, of ≦100,000 mPas.

Surprisingly it has now been found that from the reaction of uretdioneswith alcohols containing activated double bonds the desired binders canbe obtained using phenoxide salts as catalysts.

The invention accordingly provides a process for preparing binderscontaining allophanate groups which contain, at the oxygen atom of theallophanate group that is bonded via two single bonds, organic radicalswith activated groups which react, with polymerization, withethylenically unsaturated compounds on exposure to actinic radiation,where

-   one or more compounds containing uretdione groups is or are reacted    with-   one or more OH-functional compounds which contain groups which    react, with polymerization, with ethylenically unsaturated compounds    on exposure to actinic radiation, and-   optionally further NCO-reactive compounds-   in the presence of one or more compounds containing phenoxide    groups, as catalysts, and-   optionally auxiliaries and additives.

Additionally the binders obtainable by the process of the invention areprovided by the invention.

In component A) it is possible to use all organic compounds whichcontain at least one uretdione group.

Preferably these are compounds obtainable by catalytic dimerization ofaliphatic, cycloaliphatic and/or araliphatic diisocyanates orpolyisocyanates by methods which are known per se (cf. J. Prakt. Chem.1994, 336, page 196-198).

Examples of suitable diisocyanates include 1,4-diisocyanatobutane,1,6-diisocyanatohexane (HDI), trimethylhexane diisocyanate, 1,3- and1,4-bisisocyanatomethylcyclohexane, isophorone diisocyanate (IPDI),4,4′-diisocyanatodicyclohexylmethanes, 1,3- and 1,4-xylylenediisocyanates (XDI commercial product from Takeda, Japan),diphenylmethane 4,4′-diisocyanate and diphenylmethane 2,4′-diisocyanate(MDI), 2,4- and 2,6-toluene diisocyanate (TDI), or mixtures thereof.1,6-Diisocyanatohexane is preferred.

Examples of catalysts employed in this context include the following:trialkylphosphines, dimethylaminopyridines,tris(dimethylamino)phosphine.

The result of the dimerization reaction depends, in a manner known tothe skilled person, on the catalyst used, on the process conditions andon the diisocyanates employed. In particular it is possible for productsto be formed which contain on average more than one uretdione group permolecule, the number of uretdione groups being subject to adistribution. Depending on the catalyst used, the process conditions andthe diisocyanates employed, product mixtures are also formed which inaddition to uretdiones also contain other structural units, such asisocyanurate and/or iminooxadiazinedione, for example.

Particularly preferred compounds of component A) comprise products ofthe catalytic dimerization of HDI, have a free HDI content of less than0.5% by weight, an NCO content of 17-25% by weight, in particular of21-24% by weight, and a viscosity at 23° C. of from 20 to 500 mPas,preferably from 50 to 200 mPas.

The generally NCO-functional compounds obtainable by catalyticdimerization are preferably used directly as part of component A), butin principle they can also first be subjected to further reaction andonly then used in A). This further reaction may be, for example,blocking of the free NCO groups or further reaction of NCO groups withNCO-reactive compounds having a functionality of 2 or more to formiminooxadiazinedione, isocyanurate, urethane, allophanate, biuret urea,oxadiazinetrione, oxazolidinone, acylurea or carbodiimide structures.This gives compounds containing uretdione groups and of higher molecularweight, which, depending on the chosen proportions, may contain NCOgroups or may be free from NCO groups.

Blocking agents suitable for example are alcohols, lactams, oximes,malonates, alkyl acetoacetates, triazoles, phenols, imidazoles,pyrazoles and amines, such as butanone oxime, diisopropylamine,1,2,4-triazole, dimethyl-1,2,4-triazole, imidazole, diethyl malonate,ethyl acetoacetate, acetone oxime, 3,5-dimethylpyrazole, ε-caprolactam,N-tert-butylbenzylamine, cyclopentanone carboxyethyl ester or anydesired mixtures of these blocking agents. The procedure for theblocking of NCO groups is well known to the skilled worker and describedexemplarily in Progress in Organic Coatings 1999, 36, 148-172.

NCO-reactive compounds with a functionality of two or more can be theabovementioned di- and/or polyisocyanates, and also simple alcohols witha functionality of two or more, such as ethylene glycol,propane-1,2-diol, propane-1,3-diol, diethylene glycol, dipropyleneglycol, the isomeric butanediols, neopentyl glycol, hexane-1,6-diol,2-ethylhexanediol and tripropylene glycol or else alkoxylatedderivatives of these alcohols. Preferred dihydric alcohols arehexane-1,6-diol, dipropylene glycol and tripropylene glycol. Suitabletrihydric alcohols are glycerol or trimethylolpropane or theiralkoxylated derivatives. Tetrahydric alcohols are pentaerythritol or itsalkoxylated derivatives.

The compounds of component A) can be used directly in the process of theinvention or, starting from any precursor, can be prepared by priorreaction before the process of the invention is carried out.

By actinic radiation is meant electromagnetic, ionizing radiation,especially electron beams, UV radiation and also visible light (RocheLexikon Medizin, 4th edition; Urban & Fischer Verlag, Munich 1999).

Groups which react, with polymerization, with ethylenically unsaturatedcompounds on exposure to actinic radiation are for example vinyl, vinylether, propenyl, allyl, maleyl, fumaryl, maleimide, dicyclopentadienyl,acrylamide, acrylic and methacrylic groups, preference being given tousing activated groups of this kind such as vinyl ether, acrylate and/ormethacrylate groups, more preferably acrylate groups, in the compoundsof component B).

Examples of suitable hydroxyl-containing compounds of component B) are2-hydroxyethyl(meth)acrylate, polyethylene oxide mono(meth)acrylate(e.g. PEA6/PEM6; Laporte Performance Chemicals Ltd., UK), polypropyleneoxide mono(meth)acrylate (e.g. PPA6, PPM5S; Laporte PerformanceChemicals Ltd., UK), polyalkylene oxide mono(meth)acrylate (e.g. PEM63P,Laporte Performance Chemicals Ltd., UK),poly(ε-caprolactone)mono(meth)acrylates (e.g. Tone M100® Dow,Schwalbach, DE), 2-hydroxypropyl(meth)acrylate,4-hydroxybutyl(meth)acrylate, hydroxybutyl vinyl ether,3-hydroxy-2,2-dimethylpropyl(meth)acrylate, the hydroxy-functionalmono-, di- or where possible higher acrylates such as, for example,glyceryl di(meth)acrylate, trimethylolpropane di(meth)acrylate,pentaerythritol tri(meth)acrylate or dipentaerythritolpenta(meth)acrylate, which are obtainable by reacting polyhydric,optionally alkoxylated alcohols such as trimethylolpropane, glycerol,pentaerythritol, dipentaerythritol.

Likewise suitable as a constituent of B) as well are alcohols obtainedfrom the reaction of acids containing double bonds with epoxidecompounds optionally containing double bonds, such as, for example, thereaction products of (meth)acrylic acid with glycidyl (meth)acrylate orbisphenol A diglycidyl ether.

Additionally it is likewise possible to use unsaturated alcohols whichare obtained from the reaction of optionally unsaturated acid anhydrideswith hydroxy compounds and epoxide compounds that optionally containacrylate groups. By way of example these are the reaction products ofmaleic anhydride with 2-hydroxyethyl(meth)acrylate andglycidyl(meth)acrylate.

With particular preference the compounds of component B) correspond tothe aforementioned kind and have an OH functionality of from 0.9 to 1.1.

Particular preference is given to compounds containing primary hydroxylgroups, since in the process of the invention they are more reactivethan secondary or tertiary hydroxyl groups. Very particular preferenceis given to 2-hydroxyethyl acrylate and 4-hydroxybutyl acrylate.

Besides the OH-functional unsaturated compounds of component B) it ispossible in the process of the invention to use further compounds C) aswell, which are different from those of B) and contain NCO-reactivegroups such as OH, SH or NH, for example. These may be, for example, NH-or SH-functional compounds containing groups which react, withpolymerization, with ethylenically unsaturated compounds on exposure toactinic radiation.

Additionally it is possible to incorporate groups having ahydrophilicizing action, particularly if use from an aqueous medium isenvisaged, such as in an aqueous coating material, for example. Groupswith a hydrophilicizing action are ionic groups, which may be eithercationic or anionic in nature, and/or nonionic hydrophilic groups.Cationically, anionically or nonionically dispersing compounds are thosewhich contain, for example, sulphonium, ammonium, phosphonium,carboxylate, sulphonate or phosphonate groups or the groups which can beconverted into the aforementioned groups by forming salts (potentiallyionic groups) or which contain polyether groups and can be incorporatedby means of existing isocyanate-reactive groups. Isocyanate-reactivegroups of preferred suitability are hydroxyl and amino groups.

Examples of suitable ionic compounds or compounds containing potentiallyionic groups are mono- and dihydroxycarboxylic acids, mono- anddiaminocarboxylic acids, mono- and dihydroxysulphonic acids, mono- anddiaminosulphonic acids and also mono- and dihydroxyphosphonic acids ormono- and diaminophosphonic acids and their salts, such as dimethylolpropionic acid, dimethyl-olbutyric acid, hydroxypivalic acid,N-(2-aminoethyl)-β-alanine, 2-(2-aminoethylamino)ethanesulphonic acid,ethylenediamine-propyl- or butylsulphonic acid, 1,2- or1,3-propylenediamine-β-ethylsulphonic acid, malic acid, citric acid,glycolic acid, lactic acid, glycine, alanine, taurine, lysine,3,5-diaminobenzoic acid, an adduct of IPDI and acrylic acid (EP-A 0 916647, Example 1) and its alkali metal and/or ammonium salts; the adductof sodium bisulphite with but-2-ene-1,4-diol, polyethersulphonate, thepropoxylated adduct of 2-butenediol and NaHSO₃, described for example inDE-A 2 446 440 (page 5-9, formula I-III) and also structural units whichcan be converted into cationic groups, such as N-methyldiethanolamine,as hydrophilic synthesis components. Preferred ionic or potential ioniccompounds are those possessing carboxyl or carboxylate and/or sulphonategroups and/or ammonium groups. Particularly preferred ionic compoundsare those which contain carboxyl and/or sulphonate groups as ionic orpotentially ionic groups, such as the salts ofN-(2-aminoethyl)-β-alanine, of 2-(2-aminoethylamino)ethanesulphonic acidor of the adduct of IPDI and acrylic acid (EP-A-0 916 647, Example 1)and also of dimethylolpropionic acid. Suitable nonionicallyhydrophilicizing compounds are, for example, polyoxyalkylene etherscontaining at least one hydroxyl or amino group. These polyethersinclude a fraction of from 30% to 100% by weight of units derived fromethylene oxide. Suitable compounds include polyethers of linearconstruction with a functionality of between 1 and 3, but also compoundsof the general formula (I),

in which

-   R¹ and R² independently of one another are each a divalent    aliphatic, cycloaliphatic or aromatic radical having 1 to 18 carbon    atoms, which may be interrupted by oxygen and/or nitrogen atoms, and-   R³ is an alkoxy-terminated polyethylene oxide radical.

Nonionically hydrophilicizing compounds are, for example, alsomonohydric polyalkylene oxide polyether alcohols containing on average 5to 70, preferably 7 to 55, ethylene oxide units per molecule, such asare obtainable in conventional manner by alkoxylating suitable startermolecules (e.g. in Ullmanns Encyclopädie der technischen Chemie, 4thedition, volume 19, Verlag Chemie, Weinheim pp. 31-38).

Examples of suitable starter molecules are saturated monoalcohols suchas methanol, ethanol, n-propanol, isopropanol, n-butanol, isobutanol,sec-butanol, the isomers pentanols, hexanols, octanols and nonanols,n-decanol, n-dodecanol, n-tetradecanol, n-hexadecanol, n-octadecanol,cyclohexanol, the isomeric methylcyclohexanols orhydroxymethylcyclohexane, 3-ethyl-3-hydroxymethyloxetane ortetrahydrofurfuryl alcohol, diethylene glycol monoalkyl ethers such as,for example, diethylene glycol monobutyl ether, unsaturated alcoholssuch as allyl alcohol, 1,1-dimethylallyl alcohol or oleyl alcohol,aromatic alcohols such as phenol, the isomeric cresols ormethoxyphenols, araliphatic alcohols such as benzyl alcohol, anisylalcohol or cinnamyl alcohol, secondary monoamines such as dimethylamine,diethylamine, dipropylamine, diisopropylamine, dibutylamine,bis(2-ethylhexyl)amine, N-methyl- and N-ethylcyclohexylamine ordicyclohexylamine and also heterocyclic secondary amines such asmorpholine, pyrrolidine, piperidine or 1H-pyrazole. Preferred startermolecules are saturated monoalcohols. Particular preference is given tousing diethylene glycol monobutyl ether as starter molecule.

Alkylene oxides suitable for the alkoxylation reaction are, inparticular, ethylene oxide and propylene oxide, which can be used in anyorder or in a mixture in the alkoxylation reaction.

The polyalkylene oxide polyether alcohols are either straightpolyethylene oxide polyethers or mixed polyalkylene oxide polyethers atleast 30 mol %, preferably at least 40 mol %, of whose alkylene oxideunits are composed of ethylene oxide units. Preferred nonionic compoundsare monofunctional mixed polyalkylene oxide polyethers which contain atleast 40 mol % of ethylene oxide units and not more than 60 mol % ofpropylene oxide units.

Especially when using a hydrophilicizing agent containing ionic groupsit is necessary to investigate its effect on the action of the catalystD). For this reason preference is given to nonionic hydrophilicizingagents.

As compounds of catalyst component D) it is also possible, in additionto the phenoxides for use in accordance with the invention, to make usein principle of the compounds known per se to the skilled person forcatalysing the reaction of isocyanate groups with isocyanate-reactivegroups, individually or in any desired mixtures with one another.

Examples that may be mentioned here include tertiary amines such astriethylamine, pyridine, methylpyridine, benzyldimethylamine,N,N-endoethylenepiperazine, N-methylpiperidine,pentamethyldiethylenetriamine, N,N-dimethylaminocyclohexane,N,N′-dimethylpiperazine, 1,4-diazabicyclo[2.2.2]octane (DABCO) or metalsalts such as iron(III) chloride, tin(II) octoate, tin(II)ethylcaproate, tin(II) palmitate, dibutyltin(IV) dilaurate,dibutyltin(IV) diacetate and molybdenum glycolate or any desiredmixtures of such catalysts.

It is preferred, however, in D) to use exclusively phenoxides and/orcompounds containing phenoxide groups as catalysts.

The compounds of component D) containing phenoxide groups preferablycorrespond to the general formula (II),

in which

-   Z is nitrogen or phosphorus,-   R¹, R², R³, R⁴ independently of one another are hydrogen or    identical or different optionally unsaturated, substituent-bearing    or heteroatom-containing aliphatic, cycloaliphatic or aromatic    radicals having up to 24 carbon atoms and-   Y is a phenoxide radical of the general formula (III),    in which-   Q is oxygen,-   X¹, X², X³, X⁴, X⁵ independently of one another are substituents    selected from the group consisting of hydrogen, halogen, cyano,    hydroxyl, amide, amine, ether, ester, thioether, ketone, aldehyde    and carboxylate group and also optionally unsaturated,    substituent-bearing or heteroatom-containing aliphatic,    cycloaliphatic or aromatic radicals having up to 24 carbon atoms,    and optionally form parts of cyclic or polycyclic systems.

As compounds of formula (II) containing phenoxide groups it isparticularly preferred to use ammonium phenoxides and phosphoniumphenoxides and especially preferred to use tetraalkylammonium phenoxidesand tetraalkylphosphonium phenoxides.

Phenoxides preferred in particular are tetrabutylammonium4-(methoxycarbonyl)phenoxide, tetrabutylammonium2-(methoxycarbonyl)phenoxide, tetrabutylammonium 4-formylphenoxide,tetrabutylammonium 4-nitrilephenoxide, tetrabutylphosphonium4-(methoxycarbonyl)phenoxide, tetrabutylphosphonium2-(methoxycarbonyl)phenoxide, tetrabutylphosphonium 4-formylphenoxide,tetrabutylammonium salicylate and/or tetrabutylphosphonium salicylate.

It is also possible to generate the aforementioned phenoxides ofcomponent D) in situ during the process. By using the correspondingphenols and strong bases such as tetrabutylammonium hydroxide ortetrabutylphosphonium hydroxide it is possible to generate thecatalytically active phenoxides actually during the process.

It may be pointed out at this point that phenolic stabilizers ofcomponent E) may also react, by reaction with bases, to form phenoxideswhich function as catalysts for the purposes of component D). In thatcase it should be ensured that such phenoxides, in contrast to thecorresponding phenols, no longer possess any stabilizing effect. Itshould also be borne in mind that strong bases such astetrabutylammonium hydroxide or tetrabutylphosphonium hydroxide catalysethe formation of other isocyanate derivatives, especially thetrimerization.

It is also possible to apply the catalysts D) to support materials bymethods known to the skilled person and to use them as heterogeneouscatalysts.

The compounds of the catalyst component D) can be dissolvedadvantageously in one of the components participating in the process, orin a portion thereof. In particular the phenoxide salts for use inaccordance with the invention dissolve very well in the polarhydroxyalkyl acrylates, so that D) in solution in small amounts of B)can be metered in as a concentrated solution in liquid form.

In the process of the invention the catalyst component D) is usedtypically in amounts of 0.001-5.0% by weight, preferably 0.01-2.0% byweight and more preferably 0.05-1.0% by weight, based on solids contentof the process product.

As constituents of component E) it is possible in the process of theinvention to make use, for example, of solvents or reactive diluents aswell.

Suitable solvents are inert towards the functional groups present in theprocess product from the time of their addition up to the end of theprocess. Suitable solvents are, for example, those used in the paintindustry, such as hydrocarbons, ketones and esters, e.g. toluene,xylene, isooctane, acetone, butanone, methyl isobutyl ketone, ethylacetate, butyl acetate, tetrahydrofuran, N-methylpyrrolidone,dimethylacetamide and dimethylformamide, though it is preferred not toadd any solvent.

As reactive diluents it is possible to use compounds which in the courseof UV curing are likewise (co)polymerized and hence incorporated intothe polymer network and inert towards NCO groups. Such reactive diluentsare described exemplarily, by way of example, in P. K. T. Oldring (Ed.),Chemistry & Technology of UV & EB Formulations For Coatings, Inks &Paints, Vol. 2, 1991, SITA Technology, London, pp. 237-285. They may beesters of acrylic acid or methacrylic acid, preferably of acrylic acid,with mono- or polyfunctional alcohols. Examples of suitable alcoholsinclude the isomeric butanols, pentanols, hexanols, heptanols, octanols,nonanols and decanols, and also cycloaliphatic alcohols such asisobomol, cyclohexanol and alkylated cyclohexanols, dicyclopentanol,arylaliphatic alcohols such as phenoxyethanol and nonylphenylethanol,and tetrahydrofurfuryl alcohols. Additionally it is possible to usealkoxylated derivatives of these alcohols. Suitable dihydric alcoholsare, for example, alcohols such as ethylene glycol, propane-1,2-diol,propane-1,3-diol, diethylene glycol, dipropylene glycol, the isomericbutanediols, neopentyl glycol, hexane-1,6-diol, 2-ethylhexanediol andtripropylene glycol or else alkoxylated derivatives of these alcohols.Preferred dihydric alcohols are hexane-1,6-diol, dipropylene glycol andtripropylene glycol. Suitable trihydric alcohols are glycerol ortrimethylolpropane or their alkoxylated derivatives. Tetrahydricalcohols are pentaerythritol or its alkoxylated derivatives.

The binders of the invention must be stabilized against prematurepolymerization. Therefore, as a constituent of component E), beforeand/or during the reaction of components A) to D), preferably phenolicstabilizers are added which inhibit the polymerization. Use is made inthis context of phenols such as para-methoxyphenyl,2,5-di-tert-butylhydroquinone or 2,6-di-tert-butyl-4-methylphenol. Alsosuitable are N-oxyl compounds for stabilization, such as2,2,6,6-tetramethylpiperidine N-oxide (TEMPO), for example, or itsderivatives. The stabilizers can also be incorporated chemically intothe binder; suitability in this context is possessed by compounds of theabovementioned classes, especially if they still carry further freealiphatic alcohol groups or primary or secondary amine groups and hencecan be attached chemically to compounds of component A) by way ofurethane or urea groups. Particularly suitable for this purpose are2,2,6,6-tetramethyl-4-hydroxypiperidine N-oxide. Preference is given tophenolic stabilizers, especially para-methoxyphenol and/or2,6-di-tert-butyl-4-methylphenol.

Other stabilizers, such as compounds from the class of the HALS(HALS=hindered amine light stabilizers), in contrast, are used lesspreferably in E), since they are known not to enable such effectivestabilization and instead may lead to “creeping” free-radicalpolymerization of unsaturated groups.

In order to stabilize the reaction mixture, in particular theunsaturated groups, against premature polymerization it is possible topass an oxygen-containing gas, preferably air, into and/or over thereaction mixture. It is preferred for the gas to have a very lowmoisture content, in order to prevent unwanted reaction in the presenceof free isocyanate groups.

In general a stabilizer is added during the preparation of the bindersof the invention, and at the end, in order to achieve a long-termstability, stabilization is repeated with a phenolic stabilizer, andoptionally the reaction product is saturated with air.

In the process of the invention the stabilizer component is usedtypically in amounts of 0.001-5.0% by weight, preferably 0.01-2.0% byweight and more preferably 0.05-1.0% by weight, based on the solidscontent of the process product.

The ratio of OH groups from component B) to the sum of NCO and uretdionegroups from A) is typically from 1.5:1.0 to 1.0:1.9, preferably from1.0:1.0 to 1.0:1.9, more preferably from 1.0:1.0 to 1.0:1.2.

The process of the invention is preferably carried out at temperaturesof 20 to 100° C., more preferably of 40 to 100° C., in particular of 80to 89° C.

Normally the NCO groups that may be present react more rapidly with thehydroxyl groups of component B) than do the uretdione groups ofcomponent A). It is therefore possible, if two or more differentconstituents are present in B), to control the urethanization andallophanatization by means of the sequence of addition of theconstituents accordingly in such a way that one constituent of B) isincorporated preferably with urethanization while the constituent addedlast is incorporated preferably with allophanatization.

It is, however, also possible to end the allophanatization by addingcatalyst-deactivating compounds (in the case of the phenoxides, forexample, strong acids such as acidic phosphoric esters) or addingfurther isocyanate-containing compounds which scavenge the remainingcompounds of components B) and C).

It is immaterial whether the process of the invention is carried outcontinuously in for example a static mixer, extruder or compounder orbatchwise in for example a stirred reactor.

Preferably the process of the invention is carried out in a stirredreactor, the sequence of addition of components A)-E) being arbitrary.

The course of the reaction can be monitored by means of suitablemeasuring instruments installed in the reaction vessel and/or on thebasis of analyses on samples taken. Suitable techniques are known to theskilled person. They include, for example, viscosity measurements,measurements of the refractive index, of the OH content, gaschromatography (GC), nuclear magnetic resonance spectroscopy (NMR),infrared spectroscopy (IR) and near infrared spectroscopy (NIR).Preference is given to IR checking for any free NCO groups present (foraliphatic NCO groups, band at approximately ν=2272 cm⁻¹) and, inparticular, for uretdione groups (e.g. band for uretdiones based onhexamethylene diisocyanate at ν=1761 cm⁻¹) and to GC analyses forunreacted compounds from B) and C).

In one preferred embodiment of the invention there is parallelallophanatization and urethanization of the compounds of component A).For that purpose A) is introduced initially, stabilizers and, whereappropriate, further auxiliaries and additives from E) are added,subsequently components B)-E) are added and the reaction mixture isbrought to reaction temperature.

In another preferred embodiment first of all A) is reacted with B) untilthe NCO groups have reacted completely. E) or parts thereof may alreadybe present. Subsequently the reaction of the uretdione groups of A) withB) is initiated by adding D) and additionally, where appropriate, byadapting the temperature.

In one particularly preferred embodiment the isocyanate groups and theuretdione groups are reacted with an excess of hydroxyl groups ofcomponent B. The hydroxyl groups which remain following the reaction ofA) with B), with catalysis of D), are subsequently reacted preferablywith further isocyanate-containing compounds, in particular with thosecompounds described as possible constituents of component B), withurethanization.

The unsaturated allophanates obtainable by the process of the invention,in particular those based on the products—employed preferably—of thecatalytic dimerization of HDI, preferably have viscosities at 23° C. of≦100 000 mPas, more preferably ≦060 000 mPas, very preferably ≦40 000mPas.

The unsaturated allophanates obtainable by the process of the invention,especially those based on the products—employed preferably—of thecatalytic dimerization of HDI, preferably have number-average molecularweights M_(n) of from 600 to 3000 g/mol, more preferably from 750 to1500 g/mol.

The unsaturated allophanates obtainable by the process of the inventionpreferably contain less than 0.5% by weight of free di- and/ortriisocyanate monomers, more preferably less than 0.1% by weight.

The binders of the invention can be used for producing coatings andpaints and also adhesives, printing inks, casting resins, dentalcompounds, sizes, photoresists, stereolithography systems, resins forcomposite materials and sealants. In the case of adhesive bonding orsealing, however, a requirement is that, in the case of UV radiationcuring, at least one of the two substrates to be bonded or sealed to oneanother is permeable to UV radiation; in other words, in general, itmust be transparent. In the case of electron beams, sufficientpermeability for electrons should be ensured. Preference is given to usein paints and coatings.

The invention further provides coating compositions comprising

-   one or more binders obtainable in accordance with the invention,-   optionally one or more polyisocyanates containing free or blocked    isocyanate groups, which are free from groups which react, with    polymerization, with ethylenically unsaturated compounds on exposure    to actinic radiation,-   optionally other compounds, different from those of a), which    contain groups which react, with polymerization, with ethylenically    unsaturated compounds on exposure to actinic radiation, and    optionally contain free or blocked NCO groups,-   optionally one or more isocyanate-reactive compounds containing    active hydrogen, initiators,-   optionally solvents and-   optionally auxiliaries and additives.

The polyisocyanates of component b) are known per se to the skilledperson. Preference is given here to using compounds optionally modifiedwith isocyanurate, allophanate, biuret, uretdione and/oriminooxadiazinetrione groups and based on hexamethylene diisocyanate,isophorone diisocyanate, 4,4′-diisocyanatodicyclohexylmethane and/ortrimethylhexamethylene diisocyanate.

The NCO groups in this case may also be blocked, blocking agentsemployed being the compounds already mentioned in connection with thedescription of component A).

The compounds of component c) include compounds such as, in particular,urethane acrylates based preferably on hexamethylene diisocyanate,isophorone diisocyanate, 4,4′-diisocyanatodicyclohexylmethane and/ortrimethylhexamethylene diisocyanate, which optionally may have beenmodified with isocyanurate, allophanate, biuret, uretdione and/oriminooxadiazinetrione groups, and which contain noisocyanate-group-reactive functions containing active hydrogen.

NCO-containing urethane acrylates are available commercially from BayerAG, Leverkusen, DE as Roskydal® UA VP LS 2337, Roskydal® UA VP LS 2396or Roskydal® UA XP 2510.

Additionally the reactive diluents already described and known in theart of radiation-curing coatings may be used as a constituent of c),provided that they do not contain any NCO-reactive groups.

Compounds of component d) can be saturated or unsaturated. Chemicalfunctionalities reacting with NCO groups are functionalities containingactivated hydrogen atoms, such as hydroxyl, amine or thiol.

Preference is given to saturated polyhydroxy compounds, examples beingthe polyetherpolyols, polyesterpolyols, polycarbonatepolyols,poly(meth)acrylatepolyols and/or polyurethanepolyols which are knownfrom the technology of coating, adhesive bonding, printing inks orsealants and which contain no groups which react, with polymerization,with ethylenically unsaturated compounds on exposure to actinicradiation.

Unsaturated hydroxy-functional compounds are, for example, the epoxyacrylates, polyester acrylates, polyether acrylates, urethane acrylatesand acrylated polyacrylates which are known in the art ofradiation-curing coatings and have an OH number of from 30 to 300 mgKOH/g.

It is additionally possible to use the reactive diluents, alreadydescribed and known in the art of radiation-curing coatings, as aconstituent of d), provided that they contain NCO-reactive groups.

As initiators of component e) for a free-radical polymerization it ispossible to employ initiators which can be activated thermally and/or byradiation. Photoinitiators, which are activated by UV or visible light,are preferred in this context. Photoinitiators are compounds known perse, being sold commercially, a distinction being made betweenunimolecular (type I) and bimolecular (type II) initiators. Suitable(type I) systems are aromatic ketone compounds, e.g. benzophenones incombination with tertiary amines, alkylbenzophenones,4,4′-bis(dimethylamino)benzophenone (Michler's ketone), anthrone andhalogenated benzophenones or mixtures of the types stated. Of furthersuitability are (type II) initiators such as benzoin and itsderivatives, benzil ketals, acylphosphine oxides,2,4,6-trimethylbenzoyldiphenylphosphine oxide for example,bisacylphosphine oxides, phenylglyoxylic esters, camphorquinone,α-aminoalkylphenones, α,α-dialkoxyacetophenones andα-hydroxyalkylphenones.

The initiators, which are used in amounts between 0.1% and 10% byweight, preferably 0.1% to 5% by weight, based on the weight of thefilm-forming binder, can be used as an individual substance or, onaccount of frequent advantageous synergistic effects, in combinationwith one another.

Where electron beams are used instead of UV irradiation there is no needfor a photoinitiator. Electron beams, as is known to the skilled person,are generated by means of thermal emission and accelerated by way of apotential difference. The high-energy electrons then pass through atitanium foil and are guided onto the binders to be cured. The generalprinciples of electron beam curing are described in detail in “Chemistry& Technology of UV & EB Formulations for Coatings, Inks & Paints”, Vol.1, P. K. T Oldring (Ed.), SITA Technology, London, England, pp. 101-157,1991.

In the event of thermal curing of the activated double bonds, this canalso take place with addition of thermally decomposing free-radicalinitiators. Suitability is possessed, as is known to the skilled person,by, for example, peroxy compounds such as dialkoxy dicarbonates such as,for example, bis(4-tert-butylcyclohexyl) peroxydicarbonate, dialkylperoxides such as, for example, dilauryl peroxide, peresters of aromaticor aliphatic acids such as, for example, tert-butyl perbenzoate ortert-amyl peroxy 2-ethylhexanoate, inorganic peroxides such as, forexample, ammonium peroxodisulphate, potassium peroxodisulphate, organicperoxides such as, for example, 2,2-bis(tert-butylperoxy)butane, dicumylperoxide, tert-butyl hydroperoxide or else azo compounds such as2,2′-azobis[N-(2-propenyl)-2-methylpropionamides],1-[(cyano-1-methylethyl)azo]formamides,2,2′-azobis(N-butyl-2-methylpropionamides),2,2′-azobis-(N-cyclohexyl-2-methylpropionamides),2,2′-azobis{2-methyl-N-[2-(1-hydroxy-butyl)]-propionamides}, 2,2′-azobis{2-methyl-N-[2-(1-hydroxybutyl)]propionamides, 2,2′-azobis{2-methyl-N-[1,1-bis(hydroxymethyl)-2-hydroxyethyl]propionamides. Alsopossible are highly substituted 1,2-diphenylethanes (benzpinacols), suchas, for example, 3,4-dimethyl-3,4-diphenylhexane,1,1,2,2-tetraphenylethane-1,2-diol or else the silylated derivativesthereof.

It is also possible to use a combination of initiators activable by UVlight and thermally. The auxiliaries and additives of component e)include solvents of the type specified above under E).

Additionally it is possible for e), in order to increase the weatherstability of the cured coating film, to comprise UV absorbers and/orHALS stabilizers as well. Preference is given to the combination. Theformer ought to have an absorption range of not more than 390 nm, suchas triphenyltriazine types (e.g. Tinuvin® 400 (Ciba SpezialitätenchemieGmbH, Lampertheim, DE)), benzotriazoles such as Tinuvin® 622 (CibaSpezialitätenchemie GmbH, Lampertheim, DE) or oxalic dianilides (e.g.Sanduvor® 3206 (Clariant, Muttenz, CH))) and are added at 0.5%-3.5% byweight, based on resin solids. Suitable HALS stabilizers are availablecommercially (Tinuvin® 292 or Tinuvin® 123 (Ciba SpezialitätenchemieGmbH, Lampertheim, DE) or Sanduvor® 3258 (Clariant, Muttenz, CH).Preferred amounts are 0.5%-2.5% by weight based on resin solids.

It is likewise possible for e) to comprise pigments, dyes, fillers,levelling additives and devolatilizing additives.

Additionally it is possible, if necessary, for the catalysts known frompolyurethane chemistry for accelerating the NCO/OH reaction to bepresent in e). These are, for example, tin salts or zinc salts ororganotin compounds, tin soaps and/or zinc soaps such as, for example,tin octoate, dibutyltin dilaurate, dibutyltin oxide or tertiary aminessuch as diazabicyclo[2.2.2]octane (DABCO).

The application of the coating compositions of the invention to thematerial to be coated takes place with the methods known and customaryin coatings technology, such as spraying, knife coating, rolling,pouring, dipping, spin coating, brushing or squirting or by means ofprinting techniques such as screen, gravure, flexographic or offsetprinting and also by means of transfer methods.

Suitable substrates are, for example, wood, metal, including inparticular metal as used in the applications of wire enamelling, coilcoating, can coating or container coating, and also plastic, includingplastic in the form of films, especially ABS, AMMA, ASA, CA, CAB, EP,UF, CF, MF, MPF, PF, PAN, PA, PE, HDPE, LDPE, LLDPE, UHMWPE, PET, PMMA,PP, PS, SB, PUR, PVC, RF, SAN, PBT, PPE, POM, PUR-RIM, SMC, BMC,PP-EPDM, and UP (abbreviations according to DIN 7728T1), paper, leather,textiles, felt, glass, wood, wood materials, cork, inorganically bondedsubstrates such as wooden boards and fibre cement slabs, electronicassemblies or mineral substrates. It is also possible to coat substratesconsisting of a variety of the abovementioned materials, or to coatalready coated substrates such as vehicles, aircraft or boats and alsoparts thereof, especially vehicle bodies or parts for exterior mounting.It is also possible to apply the coating compositions to a substratetemporarily, then to cure them partly or fully and optionally to detachthem again, in order to produce films, for example.

For curing it is possible for solvents present, for example, to beremoved entirely or partly by flashing off.

Subsequently or simultaneously it is possible for the optionallynecessary thermal and the photochemical curing operation or operationsto be carried out in succession or simultaneously. If necessary thethermal curing can take place at room temperature or else at elevatedtemperature, preferably at 40-106° C., preferably at 60-130° C., morepreferably at 80-110° C.

Where photoinitiators are used in e) the radiation cure takes placepreferably by exposure to high-energy radiation, in other words UVradiation or daylight, such as light of wavelength 200 to 700 nm or bybombardment with high-energy electrons (electron beams, 150 to 300 keV).Radiation sources of light or UV light used are, for example,high-pressure or medium-pressure mercury vapour lamps, it being possiblefor the mercury vapour to have been modified by doping with otherelements such as gallium or iron. Lasers, pulsed lamps (known under thedesignation of UV flashlight lamps), halogen lamps or excimer emittersare likewise possible. As an inherent part of their design or throughthe use of special filters and/or reflectors, the emitters may beequipped so that part of the UV spectrum is prevented from beingemitted. By way of example, for reasons of occupational hygiene, forexample, the radiation assigned to UV-C or to UV-C and UV-B may befiltered out. The emitters may be installed in stationary fashion, sothat the material for irradiation is conveyed past the radiation sourceby means of a mechanical device, or the emitters may be mobile and thematerial for irradiation may remain stationary in the course of curing.The radiation dose which is normally sufficient for crosslinking in thecase of UV curing is situated in the range from 80 to 5000 mJ/cm².

Irradiation can if desired also be carried out in the absence of oxygen,such as under an inert gas atmosphere or an oxygen-reduced atmosphere.Suitable inert gases are preferably nitrogen, carbon dioxide, noblegases or combustion gases. Irradiation may additionally take place bycovering the coating with media transparent to the radiation. Examplesof such are, for example, polymeric films, glass or liquids such aswater.

Depending on the radiation dose and curing conditions it is possible tovary the type and concentration of any initiator used, in a manner knownto the skilled person.

Particular preference is given to carrying out curing usinghigh-pressure mercury lamps in stationary installations. Photoinitiatorsare then employed at concentrations of from 0.1% to 10% by weight, morepreferably from 0.2% to 3.0% by weight, based on the solids of thecoating. For curing these coatings it is preferred to use a dose of from200 to 3000 mJ/cm², measured in the wavelength range from 200 to 600 nm.

In the case of use of thermally activable initiators in d) by increasingthe temperature. The thermal energy may be introduced into the coatingby means of radiation, thermal conduction and/or convection, it beingcustomary to employ the ovens, near-infrared lamps and/or infrared lampsthat are conventional in coatings technology.

The applied film thicknesses (prior to curing) are typically between 0.5and 5000 μm, preferably between 5 and 1000 μm, more preferably between15 and 200 μm. Where solvents are used, it is removed after applicationand before curing, by the customary methods.

EXAMPLES

All percentages are by weight unless indicated otherwise.

The determination of the NCO contents in % was undertaken byback-titration with 0.1 mol/l hydrochloric acid following reaction withbutylamine, on the basis of DIN EN ISO 11909.

The viscosity measurements were carried out with a cone-plateviscosimeter (SM-KP), Viskolab LC3/ISO from Paar Physica, Ostfildern, DEin accordance with ISO/DIS 3219:1990.

Infrared spectroscopy was on liquid films applied between sodiumchloride plates on a model 157 instrument from Perkin Elmer, Überlingen,DE.

The amounts of trimer, uretdione, allophanate and urethane structures inthe end product were determined by means of NMR spectroscopy. For thispurpose, ¹³C-NMR spectra of a sample were recorded in CDCl₃ (DPX 400 andAVC 400 from Bruker, Karlsruhe, DE, resonance frequency 100 MHz,relaxation delay 4 s, 2000 scans, acquisition time 1.03 seconds andangle of excitation 30° C.) and the molar proportions of thesubstructures were determined from the signal integrations at δ(¹³C)=121.4 ppm (1C; NCO), 148.4 ppm (3C, trimer), 153.8 ppm (1C;allophanate), 156.3 ppm (1C, urethane) and 157.1 ppm (2C; uretdione).

The amount of residue monomers and amount of volatile synthesiscomponents were analyzed by means of GC (method using tetradecane asinternal standard, oven temperature 110° C., injector temperature 150°C., carrier gas helium, instrument: 6890 N, Agilent, Waldbronn, DE,column: Restek RT 50, 30 m, 32 mm internal diameter, film thickness 0.25μm).

The solids was determined in accordance with DIN 53216/1 draft 4/89, ISO3251.

The ambient temperature of 23° C. prevailing at the time when theexperiments were conducted is referred to as RT.

Desmodur® N 3400: HDI polyisocyanate predominantly containing uretdionestructure, viscosity 185 mPas/23° C., NCO content 21.4%, commercialproduct of Bayer AG, Leverkusen, DE.

Desmorapid® Z: dibutyltin dilaurate (DBTL), commercial product of BayerAG, Leverkusen, DE.

Darocur® 1173 photoinitiator, commercial product of CibaSpezialitätenchemie GmbH, Lampertheim, DE.

Tone® M100: reaction product of 2 equivalents of 6-caprolactone with 1equivalent of 2-hydroxyethyl acrylate, OH content=4.97%, viscosity=82mPas/23° C., commercial product of Dow, Schwalbach, DE.

Examples 1-3 describe the preparation of suitable catalytically activephenoxides, which in Examples 4-5 are used for the reaction of compoundscontaining uretdione groups with ethylenically unsaturated hydroxylcompounds to form corresponding compounds containing allophanates.

Example 1 Tetrabutylammonium 4-(methoxycarbonyl)phenoxide

A glass flask with reflux condenser, heatable oil bath, mechanicalstirrer and internal thermometer was charged at room temperature with38.00 g of methyl 4-hydroxybenzoate and 277.92 g of water and thesecomponents were stirred together thoroughly. Subsequently 162.00 g oftetrabutylammonium hydroxide (40% strength in water) were added and thereaction mixture was heated to 60° C. It was stirred at 60° C. for onehour (the contents of the flask become clear). Then the reaction mixturewas cooled and the water was distilled off under reduced pressure, 20mbar, at 30-45° C. The product was then washed with butyl acetate anddried at 80° C. and 10 mbar in a vacuum drying cabinet. This gave awhite solid.

Example 2 Tetrabutylammonium 4-formylphenoxide

A glass flask with reflux condenser, heatable oil bath, mechanicalstirrer and internal thermometer was charged at room temperature with7.64 g of 4-hydroxybenzaldehyde and 93.86 g of water and thesecomponents were stirred together thoroughly. Subsequently 40.54 g oftetrabutylammonium hydroxide (40% strength in MeOH) were added and thereaction mixture was heated to 60° C. It was stirred at 60° C. for onehour (the contents of the flask became clear). Then the reaction mixturewas cooled and the solvents (methanol and water) were distilled offunder reduced pressure, 20 mbar, at 30-45° C. The product was thenwashed with butyl acetate and dried at 80° C. and 10 mbar in a vacuumdrying cabinet. This gave a white-beige solid.

Example 3 Tetrabutylammonium Salicylate

A glass flask with reflux condenser, heatable oil bath, mechanicalstirrer and internal thermometer was charged at room temperature with35.90 g of ethyl salicylate and 282.13 g of water and these componentswere stirred together thoroughly. Subsequently 139.98 g oftetrabutylammonium hydroxide (40% strength in water) were added and thereaction mixture was heated to 60° C. It was stirred at 60° C. for onehour (the contents of the flask became clear). Then the reaction mixturewas cooled and the water was distilled off under reduced pressure, 20mbar, at 30-45° C. The residue was taken up at 60° C. in 200 ml oftoluene. Subsequently the mixture was redistilled. The residue wasrecrystallized from 50 ml of butyl acetate. The product was filteredoff, washed with butyl acetate and dried at 80° C. and 10 mbar in avacuum drying cabinet. This gave a white solid.

Example 4 Inventive Allophanate-Containing Binder

A three-necked flask with reflux condenser, stirrer and dropping funnel,and through which air was passed (6 l/h), was charged at RT with 42.70 gof Desmodur® N3400, 0.15 g of 2,6-di-tert-butyl-4-methylphenol and 0.001g of Desmorapid® Z and this initial charge was then heated to 60° C.75.72 g of Tone® M100 were slowly added dropwise, in the course of whicha maximum temperature of 70° C. was attained. Thereafter the reactionmixture was held at 70° C. until the NCO content <0.2%. Subsequently thereaction mixture was heated to 80° C. and a mixture of 31.05 g of Tone®M100 and 0.37 g of the catalyst prepared according to Example 1 wasadded dropwise. The reaction mixture was held at 80° C. until in the IRspectrum at ν=1768 cm⁻¹ uretdione groups were no longer detectable. Theproduct obtained was clear and had a viscosity of 9300 mPas/23° C., anNCO content of 0%, a trimer content of 6.5 mol %, an allophanate contentof 32.0 mol %, a urethane content of 61.5 mol % and a uretdione contentof 0 mol %.

Example 5 Inventive Allophanate-Containing Binder

A three-necked flask with reflux condenser, stirrer and dropping funnel,and through which air was passed (6 l/h), was charged at RT with 53.48 gof Desmodur® N3400, 0.08 g of 2,6-di-tert-butyl-4-methylphenol and 0.001g of Desmorapid® Z and this initial charge was then heated to 60° C.31.83 g of 2-hydroxyethyl acrylate were slowly added dropwise, in thecourse of which a maximum temperature of 70° C. was attained. Thereafterthe reaction mixture was held at 70° C. until the NCO content <0.1%.Subsequently a mixture of 15.66 g of 2-hydroxyethyl acrylate and 0.51 gof the catalyst from Example 3 was added dropwise. The reaction mixturewas heated to and held at 80° C. until in the IR spectrum at ν=1768 cm⁻¹after 3.5 h only a very weak signal for uretdione groups was detectable.0.10 g of benzoyl chloride was added and the mixture was cooled rapidlyto RT. A sample taken was found by gas chromatography to have ahydroxyethyl acrylate content of 4.15%. 6.8 g of hydroxyethyl acrylatewere added and the mixture was stirred at 80° C. until in the IRspectrum at ν=2272 cm⁻¹ there was no longer any signal for theisocyanate group. The hydroxyethyl acrylate content of a sample takenwas found by gas chromatography to be 0.07%. The product obtained wasclear and had a viscosity of 56 500 mPas/23° C. and an NCO content of0%.

Comparative Example C 1 Attempt to Prepare an Allophanate-ContainingBinder

The catalysts described in US-A 2003 301 537 13 for the crosslinking ofpowder coating materials comprising uretdione-group-containing curinggents and polymeric hydroxyl compounds without activated double bondswere examined for suitability:

Example 5 was repeated with the difference that, instead of the catalystfrom Example 3, now 0.51 g of tetrabutylammonium hydroxide was used ascatalyst. The reaction mixture was heated to and held at 80° C. until inthe IR spectrum at ν=1768 cm⁻¹ after 2 h only a very weak signal foruretdione groups was detectable. 0.10 g of benzoyl chloride was addedand the mixture was cooled rapidly to RT. In the course of this coolingthe reaction mixture turned cloudy. The hydroxyethyl acrylate content ofa sample taken was found by gas chromatography to be 2.4%. 5.20 g ofDesmodur® N3400 were added to the reaction mixture, which was stirred at70° C. until in the IR spectrum at ν=2272 cm⁻¹ there was no longer anysignal for the isocyanate group. The hydroxyethyl acrylate content of asample taken was found by gas chromatography to be 0.17%. A cloudyproduct was obtained with a viscosity of 84 000 mPas/23° C. and an NCOcontent of 0%.

Comparative Example C 2 Attempt to Prepare an Allophanate-ContainingBinder

The catalysts described in US-A 2003 301 537 13 for the crosslinking ofpowder coating materials comprising uretdione-group-containing curinggents and polymeric hydroxyl compounds without activated double bondswere examined for suitability:

Example 5 was repeated with the difference that, instead of the catalystfrom Example 3, now 0.67 g of tetrabutylammonium fluoride was used ascatalyst. The reaction mixture was heated to and held at 80° C. until inthe IR spectrum at ν=1768 cm⁻¹ after 3 h only a very weak signal foruretdione groups was detectable. 0.10 g of benzoyl chloride was addedand the mixture was cooled rapidly to RT. In the course of this coolingthe reaction mixture turned cloudy, and a colourless precipitate formed.The hydroxyethyl acrylate content of a sample taken was found by gaschromatography to be 1.7%. 4.30 g of Desmodur® N3400 were added to thereaction mixture, which was stirred at 70° C. until in the IR spectrumat ν=2272 cm⁻¹ there was no longer any signal for the isocyanate group.The hydroxyethyl acrylate content of a sample taken was found by gaschromatography to be 0.15%. A cloudy product was obtained with aviscosity of 92 000 mPas/23° C. and an NCO content of 0%.

Comparative Examples 6 and 7 show that the substances which are suitablefor crosslinking powder coating materials composed ofuretdione-group-containing curing agents and polymeric hydroxylcompounds are not suitable for the targeted synthesis of allophanatesfrom uretdiones and alcohols. The products thus obtained are clouded andof relatively high viscosity, so making them unsuitable for producingcoatings.

Example 6 Coating Formulation and Coating Material

A portion of the product from Example 5 was mixed thoroughly with 3.0%of the photoinitiator Darocur® 1173. Using a bone doctor blade with agap of 90 μm the mixture was drawn down in the form of a thin film ontoa glass plate. UV irradiation (medium pressure mercury lamp, IST MetzGmbH, Nürtingen, DE, 750 mJ/cm²) gave a hard, transparent coating whichcould not be damaged by scratching using steel wool (grade 0/0/0) in tenback-and-forth strokes with a force of 500 g directed onto the film.

Although the invention has been described in detail in the foregoing forthe purpose of illustration, it is to be understood that such detail issolely for that purpose and that variations can be made therein by thoseskilled in the art without departing from the spirit and scope of theinvention except as it may be limited by the claims.

1. A process for preparing binders containing allophanate groups whichcontain, at the oxygen atom of the allophanate group that is bonded viatwo single bonds, organic radicals with activated groups capable ofparticipating in a polymerization reaction with ethylenicallyunsaturated compounds on exposure to actinic radiation; the processcomprising reacting A) one or more compounds containing uretdione groupswith B) one or more OH-functional compounds which contain groups capableof participating in a polymerization reaction with ethylenicallyunsaturated compounds on exposure to actinic radiation, and C)optionally further NCO-reactive compounds, and D) in the presence of oneor more compounds containing phenoxide groups, as catalysts.
 2. Theprocess for preparing binders containing allophanate groups according toclaim 1, wherein the compounds of component A) containing uretdionegroups are based on hexamethylene diisocyanate.
 3. The process forpreparing binders containing allophanate groups according to claim 1,wherein component B) comprises 2-hydroxyethyl acrylate and/or4-hydroxybutyl acrylate.
 4. The process for preparing binders containingallophanate groups according to claim 1, wherein component D) comprisesas a catalyst, tetrabutylammonium 4-(methoxycarbonyl)phenoxide,tetrabutylammonium 2-(methoxycarbonyl)phenoxide, tetrabutylammonium4-formylphenoxide, tetrabutylammonium 4-nitrilephenoxide,tetra-butylphosphonium 4-(methoxycarbonyl)phenoxide,tetrabutylphosphonium 2-(methoxy-carbonyl)phenoxide,tetrabutylphosphonium 4-formylphenoxide, tetrabutylammonium salicylateand/or tetrabutylphosphonium salicylate.
 5. The process for preparingbinders containing allophanate groups according to claim 1, wherein theprocess temperatures are from 40 to 100° C.
 6. Binders containingallophanate groups and containing groups capable of participating in apolymerization reaction with ethylenically unsaturated compounds onexposure to actinic radiation, obtained by a process according toclaim
 1. 7. Binders containing allophanate groups according to claim 6,wherein the binders have a viscosity at 23° C. of ≦100 000 mPas.
 8. Amethod of preparing coatings, coating materials, adhesives, printinginks, casting resins, dental compounds, sizes, photoresists,stereolithography systems, resins for composite materials and sealantscomprising combining the binders containing allophanate groups accordingto claim 6 and one or more additives selected from the group consistingof UV absorbers, HALS stabilizers, pigments, dyes, fillers, levellingadditives, devolatilizing additives, catalysts, and combinationsthereof.
 9. Coating compositions comprising a) one or more binderscontaining allophanate groups, according to claim 6, b) optionally oneor more polyisocyanates containing free or blocked isocyanate groups,which are free from groups capable of participating in a polymerizationreaction with ethylenically unsaturated compounds on exposure to actinicradiation, c) optionally other compounds, different from those of a),which contain groups capable of participating in a polymerizationreaction with ethylenically unsaturated compounds on exposure to actinicradiation, and optionally contain free or blocked NCO groups, d)optionally one or more isocyanate-reactive compounds containing activehydrogen, e) initiators, f) optionally solvents and g) optionallyauxiliaries and additives.
 10. Substrates coated with coatings obtainedfrom binders containing allophanate groups, according to claim
 6. 11.The process for preparing binders containing allophanate groupsaccording to claim 2, wherein component B) comprises 2-hydroxyethylacrylate and/or 4-hydroxybutyl acrylate.
 12. The process for preparingbinders containing allophanate groups according to claim 2, whereincomponent D) comprises as a catalyst, tetrabutylammonium4-(methoxycarbonyl)phenoxide, tetrabutylammonium2-(methoxycarbonyl)phenoxide, tetrabutylammonium 4-formylphenoxide,tetrabutylammonium 4-nitrilephenoxide, tetra-butylphosphonium4-(methoxycarbonyl)phenoxide, tetrabutylphosphonium2-(methoxy-carbonyl)phenoxide, tetrabutylphosphonium 4-formylphenoxide,tetrabutylammonium salicylate and/or tetrabutylphosphonium salicylate.13. The process for preparing binders containing allophanate groupsaccording to claim 2, wherein the process temperatures are from 40 to100° C.
 14. Binders containing allophanate groups and containing groupscapable of participating in a polymerization reaction with ethylenicallyunsaturated compounds on exposure to actinic radiation, obtained by aprocess according to claim
 2. 15. Binders containing allophanate groupsaccording to claim 14, wherein the binders have a viscosity at 23° C. of≦100 000 mPas.
 16. A method of preparing coatings, coating materials,adhesives, printing inks, casting resins, dental compounds, sizes,photoresists, stereolithography systems, resins for composite materialsand sealants comprising combining the binders containing allophanategroups according to claim 15 and one or more additives selected from thegroup consisting of UV absorbers, HALS stabilizers, pigments, dyes,fillers, levelling additives, devolatilizing additives, catalysts, andcombinations thereof.
 17. Coating compositions comprising a) one or morebinders containing allophanate groups, according to claim 15, b)optionally one or more polyisocyanates containing free or blockedisocyanate groups, which are free from groups capable of participatingin a polymerization reaction with ethylenically unsaturated compounds onexposure to actinic radiation, c) optionally other compounds, differentfrom those of a), which contain groups capable of participating in apolymerization reaction with ethylenically unsaturated compounds onexposure to actinic radiation, and optionally contain free or blockedNCO groups, d) optionally one or more isocyanate-reactive compoundscontaining active hydrogen, e) initiators, f) optionally solvents and g)optionally auxiliaries and additives.
 18. Substrates coated withcoatings obtained from binders containing allophanate groups, accordingto claim
 15. 19. Coating compositions comprising a) one or more binderscontaining allophanate groups, according to claim 7, b) optionally oneor more polyisocyanates containing free or blocked isocyanate groups,which are free from groups capable of participating in a polymerizationreaction with ethylenically unsaturated compounds on exposure to actinicradiation, c) optionally other compounds, different from those of a),which contain groups capable of participating in a polymerizationreaction with ethylenically unsaturated compounds on exposure to actinicradiation, and optionally contain free or blocked NCO groups, d)optionally one or more isocyanate-reactive compounds containing activehydrogen, e) initiators, f) optionally solvents and g) optionallyauxiliaries and additives.
 20. Substrates coated with coatings obtainedfrom binders containing allophanate groups, according to claim 7.